﻿/*
 * qrencode - QR Code encoder
 *
 * Reed solomon encoder. This code is taken from Phil Karn's libfec then
 * editted and packed into a pair of .c and .h files.
 *
 * Copyright (C) 2002, 2003, 2004, 2006 Phil Karn, KA9Q
 * (libfec is released under the GNU Lesser General Public License.)
 *
 * Copyright (C) 2006-2011 Kentaro Fukuchi <kentaro@fukuchi.org>
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include "config.h"
#include <stdlib.h>
#include <string.h>
#ifdef HAVE_LIBPTHREAD
#  include <pthread.h>
#endif

#include "rscode.h"

/* Stuff specific to the 8-bit symbol version of the general purpose RS codecs
 *
 */
typedef unsigned char data_t;


/**
 * Reed-Solomon codec control block
 */
struct _RS
{
    int mm;              /* Bits per symbol */
    int nn;              /* Symbols per block (= (1<<mm)-1) */
    data_t* alpha_to;     /* log lookup table */
    data_t* index_of;     /* Antilog lookup table */
    data_t* genpoly;      /* Generator polynomial */
    int nroots;     /* Number of generator roots = number of parity symbols */
    int fcr;        /* First consecutive root, index form */
    int prim;       /* Primitive element, index form */
    int iprim;      /* prim-th root of 1, index form */
    int pad;        /* Padding bytes in shortened block */
    int gfpoly;
    struct _RS* next;
};

static RS* rslist = NULL;
#ifdef HAVE_LIBPTHREAD
static pthread_mutex_t rslist_mutex = PTHREAD_MUTEX_INITIALIZER;
#endif

static inline int modnn(RS* rs, int x)
{
    while (x >= rs->nn)
    {
        x -= rs->nn;
        x = (x >> rs->mm) + (x & rs->nn);
    }

    return x;
}


#define MODNN(x) modnn(rs,x)

#define MM (rs->mm)
#define NN (rs->nn)
#define ALPHA_TO (rs->alpha_to)
#define INDEX_OF (rs->index_of)
#define GENPOLY (rs->genpoly)
#define NROOTS (rs->nroots)
#define FCR (rs->fcr)
#define PRIM (rs->prim)
#define IPRIM (rs->iprim)
#define PAD (rs->pad)
#define A0 (NN)


/* Initialize a Reed-Solomon codec
 * symsize = symbol size, bits
 * gfpoly = Field generator polynomial coefficients
 * fcr = first root of RS code generator polynomial, index form
 * prim = primitive element to generate polynomial roots
 * nroots = RS code generator polynomial degree (number of roots)
 * pad = padding bytes at front of shortened block
 */
static RS* init_rs_char(int symsize, int gfpoly, int fcr, int prim, int nroots, int pad)
{
    RS* rs;


    /* Common code for intializing a Reed-Solomon control block (char or int symbols)
     * Copyright 2004 Phil Karn, KA9Q
     * May be used under the terms of the GNU Lesser General Public License (LGPL)
     */
//#undef NULL
//#define NULL ((void *)0)

    int i, j, sr, root, iprim;

    rs = NULL;

    /* Check parameter ranges */
    if (symsize < 0 || symsize > (int)(8 * sizeof(data_t)))
    {
        goto done;
    }

    if (fcr < 0 || fcr >= (1 << symsize))
        goto done;

    if (prim <= 0 || prim >= (1 << symsize))
        goto done;

    if (nroots < 0 || nroots >= (1 << symsize))
        goto done; /* Can't have more roots than symbol values! */

    if (pad < 0 || pad >= ((1 << symsize) - 1 - nroots))
        goto done; /* Too much padding */

    rs = (RS*)calloc(1, sizeof(RS));

    if (rs == NULL)
        goto done;

    rs->mm = symsize;
    rs->nn = (1 << symsize) - 1;
    rs->pad = pad;

    rs->alpha_to = (data_t*)malloc(sizeof(data_t) * (rs->nn + 1));

    if (rs->alpha_to == NULL)
    {
        free(rs);
        rs = NULL;
        goto done;
    }

    rs->index_of = (data_t*)malloc(sizeof(data_t) * (rs->nn + 1));

    if (rs->index_of == NULL)
    {
        free(rs->alpha_to);
        free(rs);
        rs = NULL;
        goto done;
    }

    /* Generate Galois field lookup tables */
    rs->index_of[0] = A0; /* log(zero) = -inf */
    rs->alpha_to[A0] = 0; /* alpha**-inf = 0 */
    sr = 1;

    for (i = 0; i < rs->nn; i++)
    {
        rs->index_of[sr] = i;
        rs->alpha_to[i] = sr;
        sr <<= 1;

        if (sr & (1 << symsize))
            sr ^= gfpoly;

        sr &= rs->nn;
    }

    if (sr != 1)
    {
        /* field generator polynomial is not primitive! */
        free(rs->alpha_to);
        free(rs->index_of);
        free(rs);
        rs = NULL;
        goto done;
    }

    /* Form RS code generator polynomial from its roots */
    rs->genpoly = (data_t*)malloc(sizeof(data_t) * (nroots + 1));

    if (rs->genpoly == NULL)
    {
        free(rs->alpha_to);
        free(rs->index_of);
        free(rs);
        rs = NULL;
        goto done;
    }

    rs->fcr = fcr;
    rs->prim = prim;
    rs->nroots = nroots;
    rs->gfpoly = gfpoly;

    /* Find prim-th root of 1, used in decoding */
    for (iprim = 1; (iprim % prim) != 0; iprim += rs->nn)
        ;

    rs->iprim = iprim / prim;

    rs->genpoly[0] = 1;

    for (i = 0, root = fcr * prim; i < nroots; i++, root += prim)
    {
        rs->genpoly[i + 1] = 1;

        /* Multiply rs->genpoly[] by  @**(root + x) */
        for (j = i; j > 0; j--)
        {
            if (rs->genpoly[j] != 0)
                rs->genpoly[j] = rs->genpoly[j - 1] ^ rs->alpha_to[modnn(rs, rs->index_of[rs->genpoly[j]] + root)];
            else
                rs->genpoly[j] = rs->genpoly[j - 1];
        }

        /* rs->genpoly[0] can never be zero */
        rs->genpoly[0] = rs->alpha_to[modnn(rs, rs->index_of[rs->genpoly[0]] + root)];
    }

    /* convert rs->genpoly[] to index form for quicker encoding */
    for (i = 0; i <= nroots; i++)
        rs->genpoly[i] = rs->index_of[rs->genpoly[i]];

done:;

    return rs;
}

RS* init_rs(int symsize, int gfpoly, int fcr, int prim, int nroots, int pad)
{
    RS* rs;

#ifdef HAVE_LIBPTHREAD
    pthread_mutex_lock(&rslist_mutex);
#endif

    for (rs = rslist; rs != NULL; rs = rs->next)
    {
        if (rs->pad != pad)
            continue;

        if (rs->nroots != nroots)
            continue;

        if (rs->mm != symsize)
            continue;

        if (rs->gfpoly != gfpoly)
            continue;

        if (rs->fcr != fcr)
            continue;

        if (rs->prim != prim)
            continue;

        goto DONE;
    }

    rs = init_rs_char(symsize, gfpoly, fcr, prim, nroots, pad);

    if (rs == NULL)
        goto DONE;

    rs->next = rslist;
    rslist = rs;

DONE:
#ifdef HAVE_LIBPTHREAD
    pthread_mutex_unlock(&rslist_mutex);
#endif
    return rs;
}


void free_rs_char(RS* rs)
{
    free(rs->alpha_to);
    free(rs->index_of);
    free(rs->genpoly);
    free(rs);
}

void free_rs_cache(void)
{
    RS* rs, *next;

#ifdef HAVE_LIBPTHREAD
    pthread_mutex_lock(&rslist_mutex);
#endif
    rs = rslist;

    while (rs != NULL)
    {
        next = rs->next;
        free_rs_char(rs);
        rs = next;
    }

    rslist = NULL;
#ifdef HAVE_LIBPTHREAD
    pthread_mutex_unlock(&rslist_mutex);
#endif
}

/* The guts of the Reed-Solomon encoder, meant to be #included
 * into a function body with the following typedefs, macros and variables supplied
 * according to the code parameters:

 * data_t - a typedef for the data symbol
 * data_t data[] - array of NN-NROOTS-PAD and type data_t to be encoded
 * data_t parity[] - an array of NROOTS and type data_t to be written with parity symbols
 * NROOTS - the number of roots in the RS code generator polynomial,
 *          which is the same as the number of parity symbols in a block.
            Integer variable or literal.
        *
 * NN - the total number of symbols in a RS block. Integer variable or literal.
 * PAD - the number of pad symbols in a block. Integer variable or literal.
 * ALPHA_TO - The address of an array of NN elements to convert Galois field
 *            elements in index (log) form to polynomial form. Read only.
 * INDEX_OF - The address of an array of NN elements to convert Galois field
 *            elements in polynomial form to index (log) form. Read only.
 * MODNN - a function to reduce its argument modulo NN. May be inline or a macro.
 * GENPOLY - an array of NROOTS+1 elements containing the generator polynomial in index form

 * The memset() and memmove() functions are used. The appropriate header
 * file declaring these functions (usually <string.h>) must be included by the calling
 * program.

 * Copyright 2004, Phil Karn, KA9Q
 * May be used under the terms of the GNU Lesser General Public License (LGPL)
 */

#undef A0
#define A0 (NN) /* Special reserved value encoding zero in index form */

void encode_rs_char(RS* rs, const data_t* data, data_t* parity)
{
    int i, j;
    data_t feedback;

    memset(parity, 0, NROOTS * sizeof(data_t));

    for (i = 0; i < NN - NROOTS - PAD; i++)
    {
        feedback = INDEX_OF[data[i] ^ parity[0]];

        if (feedback != A0)      /* feedback term is non-zero */
        {
#ifdef UNNORMALIZED
            /* This line is unnecessary when GENPOLY[NROOTS] is unity, as it must
             * always be for the polynomials constructed by init_rs()
             */
            feedback = MODNN(NN - GENPOLY[NROOTS] + feedback);
#endif

            for (j = 1; j < NROOTS; j++)
                parity[j] ^= ALPHA_TO[MODNN(feedback + GENPOLY[NROOTS - j])];
        }

        /* Shift */
        memmove(&parity[0], &parity[1], sizeof(data_t) * (NROOTS - 1));

        if (feedback != A0)
            parity[NROOTS - 1] = ALPHA_TO[MODNN(feedback + GENPOLY[0])];
        else
            parity[NROOTS - 1] = 0;
    }
}
